The invention relates to devices and methods for silencing engines. More particularly, the invention relates to devices and methods for silencing marine engines. Still more particularly, the invention relates to devices and methods for silencing marine engine wet exhaust gas using water separation techniques.
The present invention belongs to the general class of internal combustion engine exhaust silencers or mufflers that may be characterized as attempting to achieve a xe2x80x9ccold, wet/dryxe2x80x9d condition, as contrasted with a xe2x80x9ccold, wetxe2x80x9d or xe2x80x9chot, dryxe2x80x9d conditions, for extracting acoustic energy from exhaust gas. A xe2x80x9ccold, wet/dryxe2x80x9d condition is one in which a liquid coolant, typically water, first has been added to the exhaust gas of an engine, typically a marine engine, in order to reduce the temperature of the exhaust gas (the xe2x80x9ccold, wetxe2x80x9d stage), and then the water has been separated from the gas (the xe2x80x9cdryxe2x80x9d stage) in preparation for further reduction of the acoustic energy of the xe2x80x9cdryxe2x80x9d gas. The reduction in temperature is desireable for two reasons. First, the lower temperature reduces the acoustic velocity in the gas, that is, the speed at which sound propagates through the gas. The lower the acoustic velocity, the smaller the chamber that may be used to achieve a given reduction in acoustic energy, or noise. Alternatively, greater noise reduction can be achieved in a given space. Second, as the exhaust gas cools, it becomes denser. Thus, the dynamic pressure of the gas passing through a tube of a given size is reduced, resulting in a reduction in the pressure drop through the tube, and, consequently, a smaller xe2x80x9cback pressurexe2x80x9d effect. Back pressure is undesireable because it may interfere with the efficient operation of the engine or may damage it.
One undesireable attribute of cold, wet marine-exhaust silencers is that the reduction in back pressure achieved by water cooling, as just described, is offset as a consequence of the presence of water mixed with the gas. The denser net mass of the inhomogeneous water-gas mixture, as compared to a cold, wet/dry system in which the water has been removed, or as compared to a hot, dry system in which water was never added, results in an increase in back pressure. In order to avoid excessive back pressure, water-gas velocities in cold, wet exhaust systems are generally held to a range of 20 to 50 feet per second (fps). This velocity restriction places requirements on the sizes of pipes, which in some cases makes the silencers larger or less effective than desirable. Moreover, whereas in a xe2x80x9cdryxe2x80x9d gas silencer, i.e., either a xe2x80x9chot, dryxe2x80x9d or xe2x80x9ccold, wet/dryxe2x80x9d silencer, the xe2x80x9cdry gasxe2x80x9d may be conducted to a remote discharge point using a routing of both upward and downward pitched piping, such routing is often impracticable in a xe2x80x9cwetxe2x80x9d silencer because of an unacceptably large increase in back pressure for upward pitches and for corners. Because the appropriate discharge of exhaust gas from the vessel may be an important safety and convenience consideration, the limitation on discharge-pipe routing imposed by mixed water and gas discharge can impose a serious design problem or constraint.
In general, prior art marine-exhaust silencers have not optimally balanced the benefits of water cooling with the need to reduce back pressure while minimizing the size of the silencer. More specifically, some prior art marine-exhaust silencers attempt to operate in a xe2x80x9ccold, wet/dryxe2x80x9d condition but fail to achieve sufficient separation of the water from the gas. Other designs improve on such separation at the expense of large size and reduced flexibility of configuration.
For example, U.S. Pat. Nos. 5,022,877 and 4,019,456 to Harbert rely on gravitational effects and condensation to separate the exhaust gas from the water coolant, thus only partially achieving a xe2x80x9ccold, wet/dryxe2x80x9d condition. Greater separation using these means could be achieved, but at the expense of increasing the size of the silencer; i.e., by providing a larger free surface of the gas-water mixture through which the gas could rise, or at the expense of increased back pressure due to elaborate flow control. U.S. Pat. No. 4,917,640 to Miles employs such an approach by providing a more complex configuration of tubular separation chambers. Another approach, disclosed in U.S. Pat. No. 5,588,888 to Maghurious, is to agitate the wet mixture of exhaust gas and water in order to atomize the water droplets in the mixture and thereby increase the absorption of acoustic energy by the water mass. This approach is a variation of a cold, wet design in that it relies upon reduction in the acoustic energy of the exhaust gas before it is fully separated from the water, thereby incurring the penalties associated with cold, wet systems already noted.
Other techniques use waterlift silencers such as that described in U.S. Pat. No. 3,296,997 to Hoiby et al. In the Hoiby device, the mixture of cooling water and exhaust gas is introduced into a chamber through an inlet pipe. An exit tube extends vertically through the top of the chamber. The bottom of the exit tube is spaced from the bottom of the chamber so that the mixture may enter the bottom of the tube and be expelled. As described by Hoiby, the gas separates from the water in the chamber and, when the dynamic pressure in the chamber is such as to force water up the outlet tube, the level of the water surface in the chamber reduces to an extent allowing direct expulsion of gas through the tube. The kinetic energy of the gas escaping through the tube partially atomizes the water, according to Hoiby, and entrains the atomized liquid particles. The entrained liquid is thus carried, along with the exhaust gas, up through the exit tube. A similar design is shown in U.S. Pat. No. 5,554,058 to LeQuire. U.S. Pat. No. 2,360,429 to Leadbetter is one type of silencer that uses water to silence exhaust gas and includes multiple chambers.
U.S. Pat. No. 6,024,617 to Smullin et al., incorporated herein by reference in its entirety, discloses a silencer wherein a fluid mixture enters a separation chamber having an in-flow port for receiving the fluid mixture, and an out-flow port for the separated exhaust gas, and a liquid-coolant out-flow port. The separation chamber contains a separation plate having at least one dynamic separator for separating the exhaust gas from the liquid coolant by inertial or frictional effects, or both, using a series of vanes or a mesh pad.
Also, U.S. patent application Ser. No. 09/349,871 is incorporated herein by reference in its entirety. This application discloses using multiple lifting tubes, the height of the bottoms of different tubes can be differentially set, to allow the flow to be sequentially enabled in the different tubes for the purpose of generating sound attenuating benefits.
In one aspect of the invention, a silencer is disclosed that reduces the acoustic energy of a fluid mixture of a liquid coolant and of exhaust gas from an engine. The engine may be a marine engine. The silencer according to this aspect includes a receiving chamber that receives the fluid mixture, at least one lifting conduit; and a separation chamber. The lifting conduit has a receiving portion with a first opening and an expelling portion with a second opening. The receiving portion is fluidly coupled with the receiving chamber so that the fluid mixture enters the first opening from the receiving chamber and is lifted through the lifting conduit to the expelling portion. This lifting may be accomplished, at least in part, by dynamic effects. The separation chamber is fluidly coupled with the second opening of the lifting conduit, and has at least one interior surface. The at least one interior surface may include an extending member. The expelling portion of the lifting conduit is disposed so that fluid mixture expelled from the second opening is directed toward the at least one interior surface of the separation chamber. The at least one interior surface may be configured and arranged to dynamically separate at least a portion of the exhaust gas from the fluid mixture. This portion of the exhaust gas may be referred to as xe2x80x9cdry gas.xe2x80x9d The dry gas typically includes some of the liquid coolant from the fluid mixture. Also, the liquid coolant that is separated from the fluid mixture may include some exhaust gas. That is, the separation of the fluid mixture into exhaust gas and liquid coolant when the fluid mixture is expelled toward the interior surface of the separation chamber may not be a complete separation. In some implementations of the invention, the dynamic separation occurs at least in part due to linear momentum effects. In some implementations the dynamic separation occurs at least in part due to centrifugal effects.
The lifting conduit may include a first discharge pipe having a receiving portion disposed within the receiving chamber and having an expelling portion disposed within the separation chamber. The expelling portion is configured and arranged to direct the fluid mixture with an angular momentum as it is expelled and, when the fluid mixture contacts the interior surface of the separation chamber, at least a portion of the exhaust gas is separated from the fluid mixture at least in part by a centrifugal effect. The interior surface of the separation chamber may include a tubular lateral cross section. The interior wall of the separation chamber may be circular, or partially curved, so that when the fluid mixture contacts the curved surface with an angular momentum, it swirls around the interior wall. In some implementations, the expelling portion of the lifting conduit may further be configured and arranged to direct the fluid mixture with a downward momentum as it is expelled.
In some implementations, the receiving portion of the first discharge pipe may include an opening disposed at a first distance above a first surface of the receiving chamber. A second lifting conduit includes a second discharge pipe. This second discharge pipe has a receiving portion disposed within the receiving chamber and has an expelling portion disposed within the separation chamber configured and arranged to direct the fluid mixture with an angular momentum as it is expelled. When the fluid mixture contacts the interior surface of the separation chamber, at least a portion of the exhaust gas is separated from the fluid mixture at least in part by a centrifugal effect. The receiving portion of the second discharge pipe includes an opening disposed at a second distance above the first surface of the receiving chamber. The first distance may not be the same distance as the second distance. The first discharge pipe may be dynamically operative for lifting the fluid mixture when the fluid mixture has a free-surface distance above the first surface of the receiving chamber that is within a first range of distances. The second discharge pipe may be dynamically operative for lifting the fluid mixture when the fluid mixture has a free-surface distance above the first surface of the receiving chamber that is within a second range of distances including a threshold distance above which the second discharge pipe is not dynamically operative. Some other aspects of dynamic operation of the dual or multiple discharge pipes are described in U.S. patent application Ser. No. 09/349,871, referred to above and incorporated by reference herein.
The receiving chamber may, in some aspects of the invention, have a fluid mixture inlet port. The silencer in these aspects includes at least one inlet conduit having a discharge end fluidly coupled to the fluid mixture inlet port and through which the fluid mixture is received into the receiving chamber.
In some aspects, the separation chamber has at least one liquid coolant discharge port. The silencer in these aspects includes at least one liquid coolant discharge conduit, each having a receiving end fluidly coupled to a liquid coolant discharge port and through which the liquid coolant is discharged from the separation chamber.
The separation chamber may have at least one exhaust gas discharge port through which dry gas is discharged from the separation chamber. The silencer may have an expulsion chamber having at least one exhaust gas inlet port, each gaseously coupled to an exhaust gas discharge port of the separation chamber. At least one exhaust gas inlet port of the expulsion chamber and at least one exhaust gas discharge port of the separation chamber may comprise the same port. The silencer may also have one or more resonator tubes. Each of the tubes has a first portion disposed within the separation chamber through an exhaust gas discharge port of the separation chamber, and also has a second portion disposed within the expulsion chamber through an exhaust gas inlet port of the expulsion chamber. The dry gas is discharged from the separation chamber, through the one or more resonator tubes, into the expulsion chamber. In some implementations, the second portions of the resonator tubes are configured and arranged to direct the dry gas that is discharged through them into the expulsion chamber with angular momentum, a first angular momentum. Also, the lifting conduit may include a discharge pipe that has a receiving portion disposed within the receiving chamber and that has an expelling portion disposed within the separation chamber and configured and arranged to direct the fluid mixture with an angular momentum, a second angular momentum, as it is expelled. When the fluid mixture contacts the interior surface of the separation chamber, at least a portion of the exhaust gas is separated from the fluid mixture at least in part by a centrifugal effect. The second angular momentum is based at least in part on a directional component opposite to that of a directional component on which the first angular momentum is based at least in part.
The second portion of the resonator tube may be disposed so that the dry gas discharged through it is directed toward the at least one interior surface of the expulsion chamber. As noted, because prior separation typically may not be complete, the dry gas discharged through the first resonator tube may include residual liquid coolant. Additional separation of the residual liquid coolant from the dry gas may be achieved due to centrifugal effects when the dry gas is discharged from the resonator tube.
In yet additional aspects, the lifting conduit includes a dam. The two sides of the dam may be referred to for convenience as the receiving side and expelling side. Each side has first and second portions. The dam includes a directing member generally disposed across the top of the dam. The directing member may be disposed adjacent to the first portion of the receiving side so that the expelling portion of the lifting conduit includes the first portions of the receiving and expelling sides and the directing member. The first opening of the lifting conduit is disposed adjacent the second portion of the receiving side, and the second opening of the lifting conduit is disposed adjacent the first portion of the expelling side. The separation chamber has a bottom interior surface, and, in some implementations, the directing member is disposed so that the fluid mixture expelled through the second opening is directed at least partially downward toward the bottom interior surface of the separation chamber. The separation chamber may include a liquid coolant receiving chamber.
In another aspect, a method is disclosed for reducing the acoustic energy of a fluid mixture of a liquid coolant and of exhaust gas from an engine. The method includes the steps of: receiving the fluid mixture in a receiving chamber; lifting the fluid mixture through a lifting conduit; and expelling the lifted fluid mixture toward an interior surface of the separation chamber. The method may also include the further step, when the fluid mixture contacts the interior surface, of dynamically separating at least a portion of the exhaust gas from the fluid mixture. The dynamically separating step may include dynamically separating by a linear momentum effect or by a centrifugal effect. The lifting step may include dynamic lifting.
In this method, the lifting conduit may include a discharge pipe having a receiving portion disposed within the receiving chamber and having an expelling portion disposed within the separation chamber. The expelling step in this aspect may include directing the fluid mixture with an angular momentum as it is expelled. The expelling step may further include directing the fluid mixture with a downward momentum as it is expelled. Another step may be that of discharging the dry gas through one or more resonator tubes into an expulsion chamber. This step may include directing the dry gas discharged through it into the expulsion chamber with a first angular momentum. The step of dynamically separating at least a portion of the exhaust gas from the fluid mixture may include the step of directing the fluid mixture with a second angular momentum. The second angular momentum may be based at least in part on a directional component opposite to that of a directional component on which the first angular momentum is based at least in part.
In some aspects of the method, the lifting conduit includes a dam having generally opposing receiving and expelling sides each having first and second portions. The dam also has a directing member generally transverse with the receiving and expelling sides and disposed adjacent to the first portion of the receiving side. In these aspects of the method, the expelling step may include the step of expelling the fluid mixture through an expelling portion of the dam comprising the first portions of the receiving and expelling sides and the directing member. In some implementations of the method, the separation chamber has a bottom interior surface. The expelling step in these implementations further includes the step of expelling the fluid mixture through the expelling portion of the dam so that the fluid mixture is directed downward toward the bottom interior surface of the separation chamber. The separation chamber may include a liquid coolant receiving chamber.
In one aspect of the invention, a silencer is provided for reducing the acoustic energy of a fluid mixture of a liquid coolant and of exhaust gas from an engine. The silencer comprises a receiving chamber that receives the fluid mixture. At least one lifting conduit is provided having a receiving portion including a first opening and having an expelling portion including a second opening. The receiving portion is fluidly coupled with the receiving chamber so that the fluid mixture enters the first opening from the receiving chamber and is lifted through the lifting conduit to the expelling portion. A separation chamber is provided fluidly coupled with the second opening and having at least one interior surface, wherein the expelling portion is disposed so that a fluid mixture expelled from the second opening is directed toward the at least one interior surface. One or more resonator tubes are included. Each resonator tube having a first portion disposed within the separation chamber through an exhaust gas discharge port of the separation chamber and having a second portion disposed within an expulsion chamber through an exhaust gas inlet port of the expulsion chamber. At least a portion of the exhaust gas is discharged from the separation chamber, through the one or more resonator tubes, into the expulsion chamber.